Isolated Factor X Deficiency as an Immune-Mediated Complication of Waldenström Macroglobulinemia

Unexplained coagulopathy with persistent anemia presents a significant diagnostic challenge and requires a broad differential. Isolated coagulation factor deficiencies are uncommon and described only sporadically in the literature. We present a case of Waldenström macroglobulinemia (WM) resulting in isolated factor X (FX) deficiency, causing bleeding diathesis and hemorrhagic shock. This case highlights a rare but severe immune-mediated complication of lymphoplasmacytic malignancy.A 71-year-old woman with chronic kidney disease (CKD), insulin-dependent diabetes, and coronary artery disease (CAD) with recent stenting presented with weakness. She had multiple recent hospitalizations for similar symptoms, and prior evaluation revealed anemia and unexplained coagulopathy with elevated Prothrombin Time (PT)/International Normalized Ratio (INR). A hematologic workup was unrevealing until coagulation factor levels demonstrated isolated FX deficiency. An outpatient evaluation was planned, but she returned with worsening symptoms. On presentation, she had multiple hematomas involving the paraspinal muscles, abdomen, and flanks, along with gross hematuria.Given the known association between FX deficiency and amyloidosis, a fat pad biopsy was obtained following aggressive correction with fresh frozen plasma. Despite this, she developed an expanding abdominal hematoma leading to hemodynamic instability requiring vasopressors, blood products, and prothrombin complex concentrate. She underwent surgical evacuation with subsequent stabilization of the bleeding. Further evaluation revealed an elevated serum IgM (1325 mg/dL), kappa light chain level of 355.2 mg/L, and a kappa/lambda ratio of 53.82. Urine immunofixation identified a free monoclonal kappa band. Although bone marrow biopsy was deferred, MYD88 L265P mutation testing returned positive, confirming WM. The patient’s condition subsequently declined, and she was transitioned to hospice care.WM is a lymphoplasmacytic disorder characterized by clonal IgM production, immune dysregulation, and multiorgan involvement. Acquired FX deficiency is a rare complication of hematologic malignancies, usually linked to amyloidosis or plasma cell dyscrasias. The combination of WM and FX deficiency is extremely uncommon, with only one prior case described, attributed to amyloid-related adsorption. This case demonstrates FX deficiency occurring in the absence of amyloidosis, suggesting alternative immunologic mechanisms such as antibody binding or paraprotein-mediated consumption. It expands the limited literature on immune-mediated coagulation abnormalities in WM and underscores the diagnostic and therapeutic challenges encountered.